Conventionally, metallic transmission lines are widely used to transmit electrical signals or data between different components. In a high performance electronic system, since more and more processors are utilized and the signal processing speed is enhanced, it is important to enhance the quality and speed of transmitting the signals and data. However, the conventional metallic transmission lines fail to meet these requirements.
As known, there is almost no adverse influence of the material of the transmission line on the optical connection. Consequently, the optical signals may be transmitted at a high bandwidth and a high speed. Recently, the optical transmission gradually replaces the electrical transmission. For example, light emitting diodes (LEDs) and semiconductor lasers are developed by using light as a transmission medium. For example, an optical coupler is used to convert electrical signals into optical signals, convert optical signals into electrical signals, and emit and receive the electrical signals or optical signals. The optical coupler includes for example a light emitter or a light source unit for emitting optical signals, a light receiver or a light-detecting unit for receiving optical signals, or a driver circuit or an amplifier for driving or amplifying these signals.
Recently, in views of miniaturization and modularization, a system on chip (SoC) or a system-level integration (SLI) chip is developed. The system on chip technology integrates the functions of many components into a single integrated circuit (IC), so that the overall volume of the product is reduced but the applications are diversified. For example, a central processing unit includes a multi-core processor may be implemented by a SLI chip, wherein the cores have respective function and are in communication with each other and integrated into a single chip. For transmitting optical signals within the chip, the transmission paths should be elaborated designed. In particular, when optical signals are transmitted between respective chips or integrated circuits of the same circuit board, the transmission paths should be specially designed.
According to the current photoelectrical coupling, converting or transmitting techniques, an electronic component layer and a photonic layer may be either arranged at the same side of an optical transmission module or respectively arranged at different sides of the optical transmission module. The electronic component layer is a layer for operating the electrical signals or converting the electrical signals to optical signals. The transmitter and the receiver that emit and receive electrical signals or optical signals are also disposed in the photonic layer. For example, the electronic component layer is produced by a CMOS fabricating process. The photonic layer is a layer for transmitting optical signals. For example, the photonic layer is designed as a waveguide structure. In a case that the electronic component layer and the photonic layer are arranged at the same side, the units for generating or coupling electrical signals and optical signals are arranged at the same plane and connected with each other in series. Since the paths of transmitting the signals are in the same plane or the same layer, the optical signals may be emitted and received without deflection. In addition, since the fabricating processes of the electronic component layer and the photonic layer are usually different or incompatible, it is complicated to arrange the electronic component layer and the photonic layer at the same side. For example, by adding a specific material to the electronic component layer, the electronic component layer and the photonic layer may be arranged at the same side in the same fabricating process to achieve the purpose of emitting and receiving the optical signals. However, the use of the specific material is not cost-effective and the fabricating process needs to be elaborately adjusted.
In a case that the electronic component layer and the photonic layer are arranged at different sides, the transmission paths of the signals may be deflected between different layers or planes to achieve the purpose of emitting and receiving the optical signals. FIG. 1 schematically illustrates a conventional optical transmission module, in which the electronic component layer and the photonic layer are arranged at the different sides. In the optical transmission module 10, a driver circuit 16 is disposed on an integrated circuit layer 11, and upwardly connected with a light source unit 13 through a metallic line 121. The metallic line 121 is disposed within a metallic connecting structure 12. In particular, a vertical channel is formed in the metallic interconnection structure 12, and the metallic line 121 is disposed in the vertical channel to connect the light source unit 13 and the driver circuit 16. After an electrical signal is transmitted to the light source unit 13 through the metallic line 121, the light source unit 13 emits an optical signal. The optical signal is transmitted to a light-detecting unit 15 through an optical waveguide structure 14. By the light-detecting unit 15, the optical signal is converted into an electrical signal. The electrical signal is transmitted downwardly to an amplifier circuit 17 or other circuit, which is disposed in the integrated circuit layer 11, through another metallic line 122. Similarly, the metallic line 122 is disposed in another vertical channel to connect the light-detecting unit 15 and the amplifier circuit 17.
The electronic component layer and the photonic layer are separately produced by different fabricating processes and then combined together to provide the optical transmission module 10. However, it is difficult to install the metallic lines 121 and 122 in the metallic interconnection structure 12. It is also difficult to accommodate the metallic lines 121 and 122 to the fabricating processes of these two component layers. In addition, only electrical signals are allowed to pass through the metallic lines 121 and 122.
FIG. 2 schematically illustrates another conventional optical transmission module, in which the electronic component layer and the photonic layer are arranged at the different sides. In the optical transmission module 20, an integrated circuit layer 21 is upwardly connected with a light source unit 23 through metallic lines 221. For brevity, only three metallic lines 221 are shown in the drawing. The metallic lines 221 are disposed within a silicon substrate 22 and the integrated circuit layer 21. In particular, a vertical channel is formed in the silicon substrate 22 and the integrated circuit layer 21. The metallic line 221 is disposed in the vertical channels to connect the integrated circuit layer 21 and the light source unit 23. The light source unit 23 is disposed on the silicon substrate 22. After the electrical signal is transmitted to the light source unit 23 through the metallic line 221, an optical signal emitted from the light source unit 23 passes a gallium arsenide substrate 26 and is condensed by a micro lens array 27 before entering a free-space structure 24. The optical signal is then reflected by a plurality of micro mirrors 28 to be further propagated in the free-space structure 24. After the optical signal is received by a light-detecting unit 25, which is disposed on the silicon substrate 22, the optical signal is converted into an electrical signal. The electrical signal is transmitted downwardly to the integrated circuit layer 21 through another metallic line 222. Similarly, the metallic line 222 is disposed in another vertical channel to connect the light-detecting unit 25 and the integrated circuit layer 21.
Similarly, the electronic component layer and the photonic layer are separately produced by different fabricating processes and then combined together to produce the optical transmission module 20. However, it is difficult to install the metallic lines 221 and 222 in the silicon substrate. Although the light source unit 23 and the light-detecting unit 25 are flip-chip bonded to the silicon substrate 22, the free-space structure 24 should be large enough to allow the micro mirrors 28 to reflect and transmit the optical signals. In other words, the volume of the optical transmission module 20 is bulky.